The anterior third of the hypothalamus contains numerous nuclei involved in the regulation of reproductive, stress, circadian, and homeostatic behaviors. Due to the multifarious roles
of this small area, neurotransmission is diverse and variegated between the discrete functional nuclei present there. The gaseous neurotransmitter, nitric oxide (NO) has already been shown to
have an important regulatory role within the medial preoptic area (MPOA) of the anterior hypothalamus, where it serves to facilitate the expression of sex behaviors. However, little is known
about the role of other gaseous neurotransmitters in this behavioral system. Here, I report that carbon monoxide (CO), an endogenously produced gas that also acts as a neurotransmitter, also
has a functional behavioral role within this brain area in rats. The central administration of CO-facilitating molecules to the MPOA improves copulatory performance and reduces measures of
anxiety, whereas CO-inhibiting molecules serve to impair copulatory performance and increase measures of anxiety. These effects are exerted through two cellular pathways: the cyclic GMP
(cGMP) and prostaglandin E2 (PGE2) signaling systems. These pathways are somewhat distinct, with PGE2 inhibitors effectively blocking CO-induced anxiolysis but only impairing copulatory
behavior during the first sexual experience, and cGMP inhibitors effectively impairing copulatory behavior during all experiences but facilitating rather than reducing anxiolysis. These dual
mechanisms of CO signaling may stem in part from the disparate expression of the CO-producing enzymes HO-1, which is expressed transiently after the first sexual experience, and HO-2, which
increases expression only with repeated experience, as quantified by immunofluorescence. Together, these results indicate that CO has a dual behavioral role within the anterior hypothalamus,
exerting control over both reproductive and anxiety behaviors, and that its similarities and contrasts to NO may stem from the variable regulation of the two CO-producing enzymes.

Identifier:

FSU_migr_etd-9238 (IID)

Submitted Note:

A Dissertation submitted to the Department of Psychology in partial fulfillment of the requirements for the degree of Doctor of Philosophy.